1. Field of the Invention
The present invention relates to a novel N-alkylaspartyl amide derivative, a salt form thereof, a sweetening agent containing the same and a sweetened food or drink containing the N-alkylaspartyl amide derivative as an effective ingredient.
2. Discussion of the Background
With the significant societal improvements in eating habits in recent years, fatness resulting from excessive sugar intake and diseases accompanied by fatness has come under closer scrutiny. Accordingly, development of a low-calorie sweetener (sweetening agent) to replace sugar has been in increased demand. At present, aspartame has been employed owing to its excellent safety record and quality of sweetness. However, aspartame is somewhat problematic with respect to stability.
One approach to improve stability and enhance sweetening potency of aspartame is the creation of an aspartyl amide derivative by condensation of an aspartic acid and a β-aminoalcohol. The resulting product has no ester linkage. These compounds and derivatives are described in patents, such as U.S. Pat. No. 4,423,029 and EP 0203540A1 Publication, and in technical literature, such as J. Med. Chem., 13, 1217(1970) and Tetrahedron Letters, 35, 6891 (1994).
An alternative approach is described in the International Patent Publication WO 94/11391, which reports that derivatives in which an alkyl group is introduced on a nitrogen atom of aspartic acid constituting the aspartame markedly improve (enhance) the ratio of the sweetening potency and have a slightly improved stability. Of the compounds set forth in this publication, N-[N-(3,3-dimethylbutyl)-L-α-aspartyl]-L-phenylalanine 1-methyl ester, in which a 3,3-dimethylbutyl group has been employed as an alkyl group has been found to be the best. The sweetening potency of this compound is reported to be 10000 times that of sucrose. However, the sweetening potency of the other derivatives described in the foregoing publication do not exceed 2500 times that of sucrose.
A substituent group having a sweetness-enhancing effect for the aspartame equal to that of the 3,3-dimethylbutyl group therefor, has not been found. Further, examples of the derivatives in which a 3,3-dimethylbutyl group is introduced on a nitrogen atom of aspartic acid constituting an aspartyl dipeptide ester or an aspartyl dipeptide amide in place of the aspartame, are described in the FR 2719592 Publication and the International Patent Publication WO 97/29122. However, a critical need still remains to develop a method which comprises introducing a substituent group (particularly one other than the 3,3-dimethylbutyl group) on a nitrogen atom of aspartic acid constituting an aspartyl amide derivative in place of the aspartame, to obtain a derivative having a sweetening potency equal to or more than that of the N-[N-(3,3-dimethylbutyl)-L-α-aspartyl]-L-phenylalanine 1-methyl ester. Moreover, a critical need exists to develop a low-calorie sweetening agent having a superior sweetening potency compared to sucrose and/or aspartame.